Projection screen



A. B. DU MONT ET AL 0 5 9 1 uw m e s PROJECTION SCREEN Filed April 6,1946 a rfffffff Ffffffffffffffffffff fffrrrfrrrrrrrrrrrrrr rrrrrrrfrr ala I V Mfa tu 'N ENToRs Patented Sept. 5, y195() UNITED STATES PATENTOFFICE 252157112, H

PROJECTION SCREEN a Allen B. Du Mont, Upper lVIontclair, N. J.,` PaulRaibourn, Southport, Conn., and Thomas T; Goldsmith,- Jr., Cedar Grove,N.' J assignor's tov Allen B..1Du Mont Laboratores,-Inc., Passaiai NJ.,a corporation of Delaware v 'Application April y6; 1946;'seliaiNe.'660.988

This invention relates to the projection of radiant energy such as lightupon the back side of a screen in such a manner that an audience canview scenes or patterns from the front side of said screen.

By this invention radiantenergy from diiierent sources or of differentsorts, such as X-rays, infraredradiations, ultraviolet light, cosmicrays, electrons, fluorescent material excited by electrons, etc., aswell as visible light can be utilized to enable scenes or patterns to beobserved at a distance or by a large audience.

In carrying out the invention radiant venergy is caused to impinge upona target of variable density such as a picture filmer other objectthutis providedfwith a pattern so that it will modify the radiant energydistribution of the source in order to obtain the desired pattern orpicture. A screen provided with fluorescent material is uti-l lized toconvert the modiiied radiant energyinto visible light. This screencomprises a supporting layer for the fluorescent material and a Verythin layer or platinum coating having the thickness preferably of aquarter Wave length of visible light to which the human eye is mostsensitive.

The invention will be particularly described in connection withprojection of scenes or patterns from a cathode-ray screen and theprojection of moving pictures, but it is not limited tothese. With thisinvention a moving picture iil'm can be projected upon a screen andviewed byan audience Without the necessity of using the usual verystrong light. l

In carrying out the invention, ultraviolet light of differentintensities varying in accordance with the way it has been modified,such as by passing through picture film,` or as projected from acathode-ray tube screen, is projected upon a layer of material thatfluoresces upon being struck by ultraviolet light. The i'luoresence ofthis-'material varies in accordance with the different intensities ofthe ultraviolet light that strikes it and thereby produces correspondingdifferent intensities of visible light. I

The fluorescent material that is to be struck by the ultraviolet lightis applied to a very thin layer of metal which may be in microscopicparticles so that light can pass through the same. The metal layer issupported on the surface of a flat sheet of glass through which theimage is viewed.

The invention may be understood from the description in connection withthe accompanying drawing, in which:

s claims. e (o1.25o'--71) f Figjl 'is adia'gram oi elements illustratingan embodiment of the invention; and

2'is asimilardiagramy showing a modication. l f l VIn'the drawing.reference character I indicates a cathode-ray tube ofthe' sort used fortelevision purposes. -:The layer 2l on the'finside surface of thelar-'ge en'd lliofitube I is a fluorescent layer of a' ysalt that yieldsultraviolet f light in. proportion to the intensity ofthe electron beam3 that is caused' to scan it. The' layer 2 is scanned by the 'electronbeam 3 in the usual way and causes ultraviolet lightftherefrom topass-through the large-enculer this tube' l.

The ultraviolet llight from the fluorescent material 2 which'passesthrough the glass plate or support lis focussed bythe lens 6, which ispreferably madeof quartz, upon av View` screen l. This screen lcomprises a'f'clear glass plate 8 upon the back side of which; or sidetoward the lens' 6, averyl thin layer'of very small particles 910iplatinum is applied. This layer is suiii cientlyr thinto4 permit lightto pass therethrough suflicientlyeasily'torender the View appearingupon; the layer III ito'becoine'clearly'visible For example, it mayb'emade thin enough to transmit about'fO percent of the light -thatstrikes it' n "layer Itis applied to the layer 9 and consists offluorescent material of such a character that when energized or struckby ultraviolet light it-produces visible light. This light correspondsindistributionto that on the layer 'E but is much greater `inar'ea4after the conversion-'of ultraviolet light from layer 2 to visiblelight by the layerlll.` Q f In `Fig. 2'is a represented'the way toproject a moving "pictureupon a large screen by using a source'o'fultraviolet light. f

-v`In thi'sfinodiflcation a light bulb I5, which is of suchl acharacter, that it produces` ultraviolet light,l'is`used asthe 'sourceof iight that is passed through the shutter IS, which is somewhatdiagrammatically illustrated, and then through the moving picture lilmI1 that is operated in the usual way. The pictures on the lm arefocussed by lens 6 upon uorescent material I0' that is on the very thinlayer of very small particles 9 of platinum that are on the glass plateor support 8' which is the same as that described in connection withFig. 1.

The ultraviolet light from the source I5 passes through the lm Il, lens6', and is projected upon the layer I0', which liuoresces withultraviolet light, in the same way as described in connecstriking thefluorescent screen 2, has been found: Y

to increase the amount of light that is transmitted through the glass 8or 8'.

While applicants do not wish to be committed to any particular theoryfor an explanation why improved results are obtained with thisinvention, it is believed that the improved results depend largely uponthe use of the layer 9 of quarter wave thickness that is applied to theglass plate 8. This layer 9 may be platinum or it may be calciumfluoride. amount of transmitted light is obtained by minimizing ordecreasing the phenomenon known as Fresnel reilection. A layer ofquarter wave thickness of platinum or calcium fluoride may also beapplied to the outside of the glass plate 8.

-It has been known for some time that when glass is coated with a layerone-quarter of a wave length of light thickness, reilection of lighttakes place at both surfaces of such layer, and this quarter wave lengththickness causes destructive interference of the light reected from thetwo f surfaces of the layer since a diiference of length of the path ofthe light is equal to one-half of a wave length of the light. Therefore,practically all of the light passes through the glass 8 without anyappreciable amount of the light `being o reflected back toward thesource of light (Fundamentals vof Optical Engineering by Donald H.Jacobs, pp. 118 et seq., McGraw-Hill Book Company, Inc., New York). l

In other embodiments of the invention using luminescent material on asupporting surface it is advantageous to apply further thin layers ofmaterial. For example, a layer of calcium iluoride of quarter wavelength thickness may be applied between the platinum layer 9 and theglass 8. In such a case the calcium uoride layer cooperates with theblack-appearing platif num layer 9 to give the useful result ofproviding high contrast from and good light transmission through thefluorescent material l0. black-appearing layer 9 of platinum minimizesthe disturbing effects of external illumination and yet the presence ofthe layer of calcium uoride between layers 9 and 8 allows a maximumtransmission of luminescent lightthrough the assem- 2 The improvementvin the` The z 4 at this surface and improve the contrast and lighttransmission characteristics.

Some of the advantages of this invention are that it enables atelevision picture or a moving picture to be viewed upon a large atscreen even through the television picture may have been received upon asmall rounded or curved surface, and the moving picture may be upon theusual lm; the contrast between different portions of the image isimproved; the screen upon which the picture is viewed is initially darkor black due to the layer of platinum or other dark metal particles atthe back of the glass screen; the source of the visible light by meansof which the picture is seen is atthe same screen as that upon which thepicture is projected on the large scale; and the size of the picture canbe changed by changing the distance between the screen 1 and lens 6.

What is claimed is:

l. Apparatus for projecting radiant energy onto a viewing screencomprising a screen having a transparent viewing surface, a transparentmetallic layer on the back of said screen causing said screen to have adark appearance said metallic layer having a thickness about one-fourththe wave length of ultra-violet light, a layer of material, whichfluoresces when acted upon by ultraviolet light, on saidmetallic layer,and a source of ultraviolet light positioned to project said light uponsaid fluorescent layer.

2. The apparatus of claim 1 in which sai source of ultraviolet light isa cathode ray tube having a fluorescent screen for representation ofsignal intelligence.

3. The apparatus of claim l including a lm containing the picturerepresentation positioned between said source and said screen, therepresentations thereon being focussed upon said screen.

ALLEN B. DU MONT. PAUL RAIBOURN. THOMAS T. GOLDSMITH, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Williams June 11, 1946

